Electric heat treating furnaces utilize electric heating elements formed of molybdenum or graphite as radiant heat sources. The electric heating elements are usually arrayed circumferentially around the hot zone of the furnace. U.S. Pat. Nos. 5,502,742; 4,612,651; 4,559,631; and 3,812,276, the disclosures of which are incorporated herein by reference, show and describe typical arrangements of heat treating furnaces having electric heating elements .
In the known furnaces, the electric heating elements are supported from the furnace wall by hangers or support members which are attached to the furnace wall at one end and which include hardware for attaching the heating element thereto at their other end. Typically, the heating element support includes electrical insulating components so that the heating element is electrically isolated from the portion of the element support that is attached to the furnace wall. The electrical insulating components are usually formed of a ceramic material. Over time, during repeated operation of the furnace, the surface of the ceramic components becomes contaminated from materials that are dropped on them or by progressive metallization. Such contamination leads to electrical short circuits that interrupt furnace operation and can cause damage.
In electric heat treating furnaces that include forced gas cooling systems, the ceramic insulating components are subject to high stress from thermal shock which can cause cracking and failure of the component. In the furnaces, the ceramic insulating components are in direct contact with the heating element and are subject to stresses when the heating element expands or contracts during heating and cooling cycles. Furthermore, during furnace operation or maintenance, heating element supports on the bottom or hot zone floor of a furnace can be struck by falling parts or tools, which cause the ceramic components to crack or break.
Many of the known heating element supports include a support shaft that threads into the wall of the hot zone or furnace. Such a heating element support is subject to distortion and galling from thermal cycling in the furnace. That distortion and galling causes the threaded portion of the stand-off to seize, which makes the heating element support very difficult to remove when it must be repaired or replaced.
Another drawback to the known heating element supports is that they must be specifically designed for either graphite or metal heating elements because a graphite heating element is significantly thicker than a metal heating element.
In view of the foregoing, it would be highly desirable to have a support for an electric heating element in an electric heat treating furnace which overcomes the disadvantages of the known heating element supports.